Electronic counter



Sept. 4, 1951 E. GRosnol-F ELECTRONIC COUNTER Filed Feb. 1. 1949 3Sheets-Sheet 1 IVENTOR Sept. 4, 1951 E. GRosnor-'F 2,566,831 wELECTRONIC COUNTER Filed Feb. l. 1949 3 SheeCs--Sheel 2 J0 vou/765 cmg@OUA/me eiser 5* ,ff/7 ,5ms

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F. 4 75a ,4r f/,esr n Lf-L1 I l 1% 12914@ f v I@ .4b Fig .4c ffmPatented Sept. 4, 1951 nLEc'rnoNIc COUNTER Igor E. Grosdoil', Princeton,N. J., assignor to Radio Corporation of America, a, corporation ofDelaware Application February l, 1949, Serial No. 73,884

(CI. 3l833) 1o claims. l

The present invention relates to electronic counters. More particularly;it relates improvements therein including a device for controlling amechanical utilization device with the output of an nlectrcnic counter.

There are circuits. well known in the art, which operate to count cyclesof input voltages received by them, such as cycles of sinusoidalvoltages. pulses of periodic trains thereof, or sequential pulsesoccurring at random intervals. Some circuits of this type are shown anddescribed in my co-pending application Serial No. 666,472 filed on Mayl, 1946, now Patent No. 2,493,627. Such a circuit may include a numberof output terminals eachof which represents a digit or a multiple orsubmultiple of a digit which multiple or submultiple, in a decimalsystem, will be some multi? ple of ten. After the circuit counts anumber of cycles of input voltage it produces a characteristic potentialto mark the appropriate terminal representing that number. In somecounters the characteristic potential is utilized for lighting anindicator lamp which is associated with that terminal and illuminates anoverlay to produce a luminous display of the digit.

However, for certain purposes, it is desirable to utilize the positionof the marking potential (on a particular terminal) to control amechanical utilization device. For example. consider a telecommunicationsystem in which the various letters of the alphabet may be representedby different trains of voltage cycles (each including a different numberof cycles to represent a different letter). If an electronic counter beemployed at' the receiving station it would be as -desirable to employin conjunction therewith a mechanical device, such as a type-wheel,which could be rotated to place in operating position type-die of aparticular letter represented by any transmitted number of cycles.

Or consider a type of direction nding system well known in the airnavigation art. In it a ground station transmits signals in a directivebeam with which it azimuthally scans a service area. In addition, eachtime that the directional beam is pointed in a particular referencedirection, such as north, the ground station transmits(omnidirectionally) a timing pulse. In a mobile craft the timing pulseenables an electronic counter which begins to count the cycles of aperiodic voltage which is locally produced on the craft and has afrequency exactly related to the azimuthal scanning rate of thedirectional beam. Y

A receiver aboard the mobile craft is responsive when the nearest edgeof the beam reaches the mobile craft, to reduce the frequency of thelocally generated periodic voltage to one-half and is thereafterresponsive when it ceases to receive directive transmissions, i. e.,when the farthest edge of the beam passes beyond the craft, either todisable the counter or to shut oi the periodic voltage source. In thisway, the counter will indicate a number of cycles which number willrepresent the angle subtended between the reference direction, such asnorth. and the center axis of the directive radiations when it ispointed at the receiving antenna of the mobile craft. It may bedesirable for such a system that the output of the electronic countercontrol a mechanical utilization device such as a bearing indicatorhaving a needle rotatable about a circular scale calibrated according tothe points of the compass or in degrees or mills. Obviously; themechanical utilization device may be adapted to go beyond the simplefunction of indicating bearing. For example, it may operate an automaticpilot or other. suitable equipment to guide the mobile craft accordingto the bearing angle information.

It is an object of the present invention to devise a device responsiveto the output of an electronic counter to control a mechanicallyoperating utilization device.

Other objects, features and advantages of the present invention will beapparent to those skilled in the art from the following detaileddescription of an jillustrative embodiment and from the drawing inwhich:

Figure 1 is a representation of one embodiment of the present invention;

Figures 2 and 2a represent particular mechanically operatingutilizationdevices controllably by the device of the present invention;

Figure 3 shows the circuit of a. known electronic counter circuitadaptedfor use with the device of the present invention;

Figures 4, 4a. 4b and 4c are diagrams illustrating the principle ofoperation of the present device; and

Figure 5 isa. chart showing the voltage levels individually appearing onthe l0 terminals of the counter circuit (Figure 3 or block I0 of Figurel) after it has counted any number of cycles of input voltage betweenone and ten, and indicating how for any counted number of cycles betweenone and ten only one of the terminals has a potential below a certainreference level.

Where the same elements appear in more than one figure of the drawingthey are represented when it rst receives directive transmissions, i.e., by the same reference numerals.

ln Figure l` block It represents an electronic shown in Figure 3. In theexample herein the counter has l output terminals 9, I, 2-3, and is ableto count any number of cycles from one to ten. The number of outputterminals may be increased or decreased according to the requirements ofany particular situation` For example. if the device of the presentinvention is used for controlling a bearing indicator the scale of whichis divided by 36 calibrations into increments of ten degrees theelectronic counter may be expanded accordingly to the principles setforth in the above-mentioned co-pendingapplication to have 36 outputterminals, or if desired, a tenterminal counter. such as counter I0, maybe ntted into a decimal system wherein it counts the digits of thedecimal system (and, as will be shown herein, sets a mechanicalutilization device to represent them) and wherein, in addition, itproduces one output voltage cycle for each full count of ten to actuatea second ten-terminal counter, i. e., a following decada which countsthe tens of cycles and sets a second mechanical utilization deviceaccording to the present invention.

An automatic selector switch II has ten circumferentially positionedcontacts 0a, Ia, 2a-9a each of which is connected to a different one ofvthe output terminals, D-S. of the counter I0.

. sequentially around the. circumference of the The contacts Ila-9a aremounted switch Il. around the circumference of switch I0 withinsulation, such as air, between them so that adjacent ones do not makelow impedance contact with each other. However, each contact isconnected over a high impedance element to the contact adjacent to it oneach of its two sides. The high impedance elements shown in Figure 1 are10 resistors 0b, Ib-Sb, all of which preferably have the same value ofresistance.

rPhe connection between each of the terminals 0-9 and its correspondingselector switch contact Uil-9. is made over a different one of a groupof 10 diodes llc-9e which is connected with its cathode side toward thecounter. The anode of each of the diodes 09 is positively biased byconnection to a respective one of ten biasing voltage dividers Ila-9d,each or which is grounded on its lower end: is connected to a source ofpositive voltage, B+, at its upper end; has an intermediate pointconnected to the diode anode. equivalent to the voltage level which isobtained a-t a junction point to which each of the anodes of apreselected three tubes of the decade counter Il are connected throughequal individual resistors when the voltages at two of the anodes arereduced below B+ because the tubes in which they are included aredrawing current and the third anode is at or near B+ because the tube inwhich it is included is cut oil. Because of this. this bias level willbe referred to herein as the level It will be seen that whenever thecounter circui-t I0 has counted a number of voltage cycles within itscounting range each of its output terminals 0-9 will be at one of fourpossible potential levels to be explained more fully hereinafter.- Twoof these possible potential levels will be above the bias level vandwill be referred to herein as and one of them will be the bias level andone of them below it. i. e.,

This bias level is level Each in the designation of a possible level fora terminal means that the terminal is connected to the anode of amultivibrator tube which is drawing current and each means that it isconnected -to the anode of a tube which is cut off. After any count of aparticular single terminal, and no other, will be marked with the leveland that terminal will represent the number counted.

It is apparent from the arrangement shown in Figure 1 that all of thediodes llc-9c, except the one connected to a terminal marked with thepotential, will have their cathodes more positive than their anodes andtherefore will introduce infinite impedances 'between the unmarkedoutput terminals and their respectively corresponding selectorswitch.contacts. In the one oase oi the marked terminal the diode-cathode will be below the bias level of its anode .and therefore currentwill tlow from ground through the lower resistor of its biasing bleeder(one of the IIa-9d bleeders) through the diode and into the countercircuit, thus dropping the potential of the corresponding contact (oneof the IIa-9| contacts). Since all of the lla-9. contacts areinterconnected by the resistors lib-9s and since each of them isconnected to ground over the lower resistor of its associated biasingbleeder, there will be ten parallel ground return paths contributing tothe flow of current from the marked selector switch contact toward thecounter circuit. 'I'his will produce two symmetrical voltage gradientsaround opposite sides of the circle of selector switch contacts from themarked contact (most negative) to the contact positioned oppositely toit in the ring (least negative). 0n each side successive contactsbetween the marked one and the opposite one will be progressively lessand less negative. It is upon the existence and angular orientation ofthis gradient that the operation of the present device depends.

Selector switch II comprises a rotatable hub I2 which may be ofinsulating material. Fastened to the hub I2 at their respective innerends are two oppositely extending radial arms I 3 and I4 which carry a-ttheir respective outer ends two arcuate brushes I5 and I6. Thus, if thebrush carried by one of these two arms is positioned to engage themarked contact, the brush carried by the opposite arm will be positionedto contact 4the oppositely positioned contact in the circle of theselector switch.

The arms I3 and I4 may be of conductive material, or, if not, theyshould comprise conductors extending lengthwise of them for electricallyconnecting the brushes which they carry to respective slip rings I'I,I8. The arm Il is provided with a wiper brush I9 for electricallycontacting the slip ring II and the arm I4 is provided with a brush 20for similarly engaging the slip ring I8. Fastened to the hub l2 in aposition angularly displaced to one side of the arm I3 in acounter-clockwise direction is a selector arm 2| carrying a selectorbrush 22 of such size and shape that when the arcuate brush I5 fullyengages any of the selector switch contacts, the selector brush 22 willfully engage the seleclor switch contact adjacent thereto in acounterclockwise direction. The arm 2l is provided with a slip ringbrush 23 for engaging a slip ring 24. Fastened to the hub I2 in aposition angularly displaced from the arm I3 on its side opposite to thearm 2l is a second selector arm 25 carrying a selector .brush 26 so thatwhen arcuate brush I5 fully engages any of the selector switch contacts,li-I., the selector brush 2l will fully engage the selector contactadjacent thereto in a clockwise direction. The selector arm 2l has aslip ring brush 21 cooperating with a slip ring 23. A main relay 3l isconnected to the slip rings 2l and 23 over a D. C. ampliiler 3l. Themain relay 3l is a polarized relay operating an arrangement 32 of twoarmatures and four contacts which comprises a double-pole double-throwswitch. The two armatures oi the arrangement 32 are electricallyconnected to a reversible D. C. motor 33 and th'e i'our contacts o! thearrangement 32 are connected to a D. C. power source 3l. Theseconnections are so made. according to well known practices. that whenthere is' a voltage diilerence between selector brushes 22 and 2l (dueto the existence of two potential gradients around opposite sides of thecircular selector switch and non-symmetrical positioning of thesebrushes thereon) the main relay 33 will be actuated to connect the D. C.power source 34 to the reversible motor 33 in either of two polarities(depending on the polarity of the voltage difference) for operating themotor in either of two directions.

A mechanical linkage 3i interconnects the shaft ofthe reversible motorwith the hub l2 of the selector switch I I so that whenever the motor 33operates, hub I2 will be rotated and will carry with it'the four armsI3. il. 2i and 28 and with them their associated arcuate brushes (i5,I3), selector'brushes (22, 23), wiper brushes (i3, 2l). and slip ringbrushes (23, 21). It is obvious that this electro-mechanical system caneasily be put together so that for either polarity of a voltageditlerence which exists between the selector brushes "22 and 26 the hubi2 will be rotated in a direction to move the arcuate brush il towardthe selector switch contact marked with the potential level An auxiliaryrelay 33 is employed herein because without it there is a one possiblecondition in which this device would be inoperable. This condition wouldexist when one cycle of operation, in which the arcuate brush II hasbeen positioned on a particular selector switch contact, is followed byanother cycle in which the counter l0 upon completing its count happensto mark (with the potential level the exactly oppositely positionedselector switch contact. In this case there would be no overallpotential difference between the selector brushes 22 and 26 because twoequal and opposite voltages of opposite polarity would respectivelyexist between the respective contacts which they engage and the onecontact located between them, and these two voltages would oppose andexactly balance each other. The auixiliary relay 36, which is alsorofthe polarized time. has its magnetizing coil connected between the sliprings l1 and I3. It comprises an arrangement 31 of two armatures andfour contacts utilized, as shown in Figure 1 so that when the relay isactuated in one direction it is ineiectual, whereas when it is actuatedin another direction it applies power from the source 34 to the motor 33in appropriate polarity to cause it to rotate the hub i2 in thedirection to move the selector brushes 22 and 26 into engagement withselector switch contacts which will provide a gradient between them ofthe proper polarity to operate the main relay 33 to continue theoperation ot the motor 33 in the same direction.

The main relay 3l, in addition to its doublepole double-throwarrangement 32. comprises an 8 auxiliary-relay-disabling arrangement 3lincluding an amature and two spring arms oppositely deilectable by thearmature and respective contacts for the spring arms so that inwhichever direction the main relay 3l is operated, the arrangement 31acts to disable the energizing circuit of the auxiliary relay. Thus. ifa cycle o! mechanical operation is started by the auxiliary relay 33, itwill only retain control over the operation of the motor -33 until themain relay 3l is actuated. Obviously, on the other hand, if a cycle isstarted by the main relay the auxiliary relay will not be able to assumecontrol during any portion oi the same operating cycle. In theembodiment shown herein a D. C. ampliiier 33 is included in series withthe magnetizing coil of the auxiliary relay 33.

Block 33 represents a mechanically operated utilization device which isactuated synchronously with the hub i2 whenever it is turned by themotor 33. As shown in Figure 2. this utilization device may be atype-wheel 40 which is mechanically rotatable by the electro-mechanicalFigure 3 shows the circuit details o! an embodiment of a voltage cyclecounter (block Il of Figure 1) adapted for use in the present invention.It comprises four multivibrators MV-L liv-2, MV-3, MV-I whoseinterconnections and internal circuit arrangements are shown and'i'ullydescribed in my co-pending application Serial No. 666,472, now PatentNo. 2,493,627 (see Figure 4 of that application and note the fourmultivibrators Mv-L Mv-z, Mv-s, Mv-l and the eight anodes I', 2'-3'thereof which are shown in that ligure and correspond to the similarlydesignated elements of Figure 3 herein) As explained therein, each ofthe anodes i'3' will at any time be at one of two possible potentiallevels, one an upper level at or near the level of the source energizingthe multivibrators and the other a lower level well below it. Any anodewill assume the upper level when its tube is cut oi and the lower levelwhen it is drawing considerable current. For example, as shown in Figure6d therein. plate l' alternates between the upper and lower levels fivetimes as the circuit counts from zero cycles up to 9. As shown in Figure6c therein and as should be expected inasmuch as it is included in thesame multivibrator with anode l', anode 2' is at the low level whenplate l is at the high level and vice versa. As also appears in Figure6d of the co-pending application, plate 3 is at the high level after thecounting of zero cycles, one cycle, six cycles, or seven cycles. and itis at its low level after the counting of 2. 3, 4, 5, 8 or 9 cycles. Asshown in Figure 6A therein, and as should be expected since it is aportion of the same multivibrator as anode 3', anode 4' is at the lowlevel whenever plate 3 is at the high level and vice versa. Similarinformation about the conditions of plates 5", 8', 'l' and 3' appear inFigures 6E, 6C, 6H and 6A. The group of resistors A shown in Figure 3herein to the right of the heavy vertical line representing a bus wirefor supplying B+ to the tubes of the multivibrators are used forconnectingy each of. the terminals l-l toal particular combination ofthree of the anodes I'I. According to principles described in theabove-mentioned co-pending application, and illustrated in the Figures(iA-6J and 7 therein, this arrangement results in marking only aparticular one of the terminals 6-9, with the marking potential for eachcompleted count'as well as in the orderly progression o! thispotentiai'aiong the line oi' contacts from 6 to 9 as successively highernumbers of cycles are counted from 0 (zero) to 9. For example, terminalI is connected over re-three individual resistors to the anodes I. 5'and 6' and therefore for any condition of the circuit, i. e., after ithas completed any count up to 9, the potential of terminal 5 will bedetermined by the potentials of these three plates as combined over theresistors. For a count of five. terminal 5 will be marked with themarking potential, inasmuch as all of the anodes to which it isconnected will be at their low levels.

The detailed arrangement counting circuit shown'in Figure 3 does notconstitute the present invention and therefore need notbe described morefully herein. Further description of its principles of operation can befound in another ,of myco-pending applications, Serial No.

580,446 filed March l, 2.521.788.

Figure 5 shows the voltage level produced on each of the terminals 0-9of a voltage counter of the Skind shown in Figure 3: (1) when it has notcounted any cycles of input voltage (when it has counted zero cycles);(2) when it has counted one cycle of input voltage; (3) when ithas-counted two cycles of input voltage; etc., up

1945, now Patent No.

to nine cycles. It will be seen, for example, that when the voltagecounter has counted 5 cycles of input voltage the potential level willappear on the output terminals 0, 2, 1 and Il;4

the potential level will appear on the terminals l, 3, 4 and 9; thepotential level -I- will appear on the terminal 6; and the potentiallevel i. e., the marking potential level, willap'pear only on terminal5. However, due to the use of the biased diodes Ile-9c in theinterconnections between the output terminals of difference across thebrushes I6 and Il. However, the polarity of this potential dillerencewould be such as to actuate the auxiliary relay in its ineilectualdirection and the overall eilect would be that motor Il would not beoperated.

In Figure 4a the condition shown in Figure 4 is changed by a factor of180, the marked contact is directly opposite to the position o! brushl5. At the outset the main relay would not tend to be energized, asthere would be no voltage difference between the selector brushes 22 and26 (see above explanation of the reason for including the auxiliaryrelay 26). However,

the voltage diilerence between the brushes Il and I6 would be such as tooperate the auxiliary relay in its effectual d.rection, thus actuatingthe motor and rotating the hub I2 in a direction which wouldprogressively reduce thevoltage drop across the auxiliary relay butwould l'move the selector brushes 22 and 26 into engagement withcontacts between which there `would exist a suitable potential diierencefor operating the main relay in a direction appropriately to actuate themotor to Vcontinue the hub movement which was started by the action ofthe auxiliary relay.

Figure 4b shows a condition 90 diierent from that of Figure 4 or fromthat of Figure 4a. In thisl situation, the auxiliary relay will not beactuated; however, a potenial diilerence will exist between the selectorbrushes 22 and 26 and it will be of the polarity for actuating thepolarized main relay in a direction to operate the motor to drive thearcuate brush I5 in the direction of the marked selector switch contact.When the main relay operates to do this it will at the same time disablethe auxiliary relay which therefore will not operate at all for thisparticular counting cycle.

Figure 4c shows a situation 180 diierent from the situation of 4b. Inthis instance also the auxiliary relay will not be actuated. However,the polarity of the voltage difference between the selector brushes 22and 26 will be such as to operate the main relay in the oppositedirection from that in which it is operated under the conditions ofFigure 4b and thereforethe hub I2 of the selector switch will be rotatedin an opposite direction and again the arcuate brush I5 will move towardthe marked selector switch contact.

the voltage counter and respective contacts u (iv-9. of the selectorswitch` I I. only the marking potential will be transferred from thevoltage counter I0 to the selector switch 36 and for any count thiswill. be a potential applied irom-'only one output terminal to only onecontact.

Figures 4, 4a, 4b and 4c schematically repre- .fent the manner ofcooperation of the main and auxiliary relays 30 and 36 for a number oflimiting conditions. In all of these figures a straight arrow representselectrical current; a curved arrow represents hub rotation: anddotted-line arrows represent currents and rotation which take placelater than the start of a cycle of operation of switch Il. In Figure 4the condition is shown in which the selector switch is already properlyset for the position of the marking potential applied to it by thecounter Iii, i. e., a condition arising from the fact that the countmade in the preceding cycle of operation was the same one. potentialdifference between the selector brushes 22 and 26 and therefore the mainrelay would not be actuated. There would be a potential In this case.there would be no- I claim as my invention: 1. A selector switcharrangement comprising I an electrical loop of series-connectedalternatelyoccurring contacts and resistors, the resistors all havingsubstantially the same value, a source of reference potential, a groupof second resistors each of which is equal in resistance value to all ofthe other second resistors and each of which is connected between'adiierent respective one of said contacts and said source of referencepotential, means for selectively generating separate potentialsincluding a marking potential. a group of rectifiers, one end of each ofsaid rectiilers being coupled to a respective one of said contacts. theother end of each of said rectiilers being coupled to said means forgenerating separate potentials to receive one of said potentials. thevalue of said source of reference potential being selected to permitonly said rectier to which said marking potential is applied to beconductive whereby a marking potential is applied to the contact towhich said conductive rectier is coupled. a pair of selector brushesdisposed for simultaneously engaging respective non-adjacent ones of thecontacts, and control means responcontact for relatively moving thebrushes respect to the contacts toward a positionsh'addletbemarkedcontact.

othersecondresistorsandbetweenaYliiil'erentrespectiveonleotlsaitdcontacandsaicl source of referencepotential, means for selecvelygenerating separate potentials includingamarkingpotenalagroupofrectiiieraonecndofeachofsaidrecidilcrsbeingcoupledtoarespectiveoneotsaidcontactatheotherendoi'cachotsaidrectiiiersbeingcouplcdtosaid potential is applied to thecontact to which said conductive rectier is coupled, a pair of selectorbrushes rotatably with respecttothecenteroithecircleiormedbysaid.

contacts with t angular separation between them for simultaneously grespective non-adjacent ones ot the contacts. controlmeansresponsivetotheapplicationoiamarking` theconiaetinaclockwisedirectionthusinacountcrclockwise ried within the circle with suiiicientangular separation between them for simultaneously engaging respectivenon-adjacent ones of the contacts. means responsive when said markingpotential is applied to one of the contacts for rotating the brushes inunison to hunt in either direction around the circle of contacts towarda position where one oi them is on one side of the marked contact and isangularly distant therefrom by one half of said angular separation andthe other is on its opposite side.

4. The selector switch arrangement as described in claim 3 in which saidlast-mentioned means is unresponsive if, at the time when the markingpotential is applied to a contact, said one and said other brushes arerespectively on said opposite and said one sides thereof, and includingmeans responsive if this condition exists when said marking potential isapplied to start the rotation oi the brushes until said last-mentionedmeans does becomes responsive.

5. The selector switch arrangement described in claim- 4 lin which the`added means recited in that claim comprises a pair of arcuate brushesrotatably carried within the circle on opposite sides thereof forrespectively engaging two contacts oppositely positioned in said circle,each arcuate Abrush being positioned with equal angular separation fromeach selector brush, and a polarized relay coupled across the arcuatebrushes and responsive to the voltage diiierence therebetween when saidcondition exists. and the selector switch arrangement further includesmeans for disabling the polarized relay when the means for rotating theselector brushes becomes responsive.

6. A selector switch arrangement comprising a plurality of contactsplaced side by side-in a circle, an equal plurality oi impedance devicesall having at least approximately the same impedance value, means forinterconnecting each two adjacent contacts over a diiierent one of theimpedance devices, means for applying a reference potential tov each ofsaid contacts including an equal plurality of second impedance deviceshaving among themselves approximately equal values of impedance, each oisaid contacts being connected to ground over a different one of saidsecond impedance devices, means for applying a marking potential to oneof said contacts to produce voltage gradients around both sides of thecircle of said contacts from said one contact to the contact opposite itin the circle. a pair of selector brushes,` a support rotatably carrylngthe brushes with angular separation so that they can respectively engagesimultaneously two non-adjacent ones of said contacts, means forrotating said support to cause said brushes to hunt in unison in eitherdirection around the circle of contacts to the one of two possiblepositions in which they straddle the marked contact in which oneposition the angular distance as measured from a predetermined one ofthe brushes to said contact is shorter in a clockwise direction than ina counter clockwise direction, a polarized relay with its magnetizingcoil coupled across said selector brushes and arranged to be responsiveto a potential of one polarity therebetween to actuate said means forrotating to cause said brushes to hunt in one direction and to apotential of opposite polarity to actuate said means for rotating tocause said brushes to hunt in the opposite directio'n.

'1. A selector switch arrangement comprising a plurality of contactsplaced side by side in a circle, an equal plurality of iirst resistorsall having 'approximately the same value ofresistance, nieans forinterconnecting each two adjacent contacts over a different one of theresistors. means to apply reference potentials to each of said contactsincluding an equal plurality of second resistors having among themselvesapproximately equal values of resistance, each of said contacts beingconnected to ground over a different one of said second resistors, meansfor selectively generating separate potentials including a. markingpotential, an equal plurality of rectiilers, each of said rectifiersbeing connected berectier to produce voltage gradients around 1l bothsides of the circle oi contacts from the marked contact to the contactopposite to it in the circle, a pair of selector brushes. a supportcarrying the brushes rotatably within the circle with angular separationbetween them so that they can simultaneously engage two respectivenon-adjacent ones of said contacts, means for rotating the brushes inunison to hunt in either direction around the circle of contacts, apolarized relay with its magnetizing coil coupled across said brushesand arranged to be responsive to a potential of one polaritytherebetween to actuate said last mentioned means to cause said brushesto hunt in one direction to a position to the one of two possiblepositions in which they straddle the marked contact in which oneposition the angular distance as measured from a particular one ofthebrushes to said contact is shorterin a clockwise than in a counterclockwise direction, and to be responsive to a. potential of oppositepolarity therebetween to actuate said last-mentioned means to cause saidbrushes to hunt in the opposite direction to said one positicn.

8. A selector switch arrangement comprising a loop of series-connectedaltemately-occurring contacts and resistors, the contacts being placedside by side in a circle and therresistors all having substantially thesame value, an electronic voltage-cycle' counter which comprises aninput circuit and as many output terminals as the number of saidcontacts and is responsive to a number of cycles of input voltage toproduce a predetermined marking potential on a particular one of saidoutput terminals which corresponds to that number Yand also to produceother potentials on the other output terminals, said .marking potentialbeing distinguishable from said other potentials by the fact that itsmagnitude and theirs have opposite relationships to the magnitude of areference potential, an individual circuit connecting each of saidoutput terminals to one of said contacts, each individual circuitincluding in series a diode and a means for blasing one of theelectrodes of the diode to said reference potential, the diode andbiasing means of any individual circuit being arranged in it so that thediode will be cut oi when any'of said other potentials is applied to itsoutput-terminal end, but will pass current when said marking potentialis applied thereto, `said biasing means including a group of secondresistors each of which is equal in resistance value to all the othersand is connected between a respective one of said contacts and ground, apair of selector brushes rotatably carried within the circle withangular separation so that they respectively engage non-adjacent ones ofsaid contacts, and means responsive when the counter circuit applies amarking potential to one of said contacts for rotating the brushes inunison to hunt in either direction around the circle of contacts towarda position lwhere one of them is on one sidev of the marked contact andis angularly distant therefrom by one hal! of said angular separationand the other is on its opposite side. Y

9. A selector switch arrangement comprising an electrical loop ofseries-connected alternatelyoccurring contacts and resistors, theresistors all having substantially the same value, a plurality ofrectiers, means for selectively generating separate potentials,including a marking potential, one end of each of said rectitlers beingcoupled to one of said contacts, the other end of each of saidrectiiiers being coupled to said selective generating'means to receiveone of said separate potentials, means to apply a reference potential toall said rectiilers at said one end of a value to permit only saidrectier to which said marking potential is applied to be conductive,whereby a marking potential is applied to the contact to which saidconductive rectifier is coupled, a pair of selector brushes disposed forsimultaneously engaging respective non-adjacent ones oi the contacts,and control means responsive to a voltage difference between the brushesdue to the application of a marking potential to a contact forrelatively moving the brushes with respect to the contacts toward aposition to straddle the marked contact. i

10. A selector switch arrangement as described in claim 2 wherein saidcontrol means includes an auxiliary pair of brushes angularly disposedwith reference to said pair of selector brushes and rotatably disposedwith reference to the center of the circle formed by said contacts, saidauxiliary brushes being rotatable with said selector brushes, firstrelay means responsive to a potential diierence between said auxiliarypair of brushes for energizing said control means to rotate saidselector brushes and second relay means connected to said control meansto hold said first relay means unresponsive when said control means areresponsive to a potential applied to said selector brushes.

IGOR E. GROSDOFF.

REFERENCES CITED The following references are of record in the le ofthis patent:

l UNITED STATES PATENTS Number

